The present invention relates generally to the field of mail extraction, and in particular, to certain improvements in the so-called "candling" of envelopes in connection with their processing by a mail extraction device.
A variety of devices have been developed to facilitate the mail extraction process, in which large quantities of envelopes are automatically opened to gain access to their contents. One example of this is the "Rapid Extraction Desk" manufactured by Opex Corporation of Moorestown, N.J., an exemplary model of which is illustrated in U.S. Pat. No. 3,979,884 (Re 32,328).
In their overall operation, these machines are used to receive a series of envelopes which are first sequentially delivered to a device for severing (cutting open) one or more envelope edges, and which are then sequentially delivered to an extraction area for access by the machine's operator. At the extraction area, steps are taken to spread apart the opposing faces of the envelope, permitting the operator to gain access to the contents of each envelope for extraction. The emptied envelope is then released from the extraction area, and checked to make sure that the envelope has been emptied of all of its contents.
In operating these machines, it is often important to determine if documents are contained by the envelope as it passes through the mail extraction device. For example, it has for some time been common practice to sequence operations of the mail extraction device responsive to an extraction of documents from the envelope by the machine's operator. Such so-called "content activation" (as well as "differential activation") is particularly useful in increasing the efficiency of the mail extraction procedure by conveying envelopes to and from the extraction point at a rate which is suited to the operator, yet as rapid as possible. It has also for some time been common practice to check each envelope following the extraction procedure, to verify that all contents have been removed before the envelope is discarded.
Each of these functions are performed by what can generally be characterized as a "candling" operation, in which steps are taken to "look through" an envelope by monitoring changes in the envelope's ability to transmit light (either from an applied source or making use of ambient lighting). This is then used to initiate one or the other of the above-identified system functions, as desired.
It has for some time been known that the transmissivity of an envelope, and accordingly, the ability of conventionally available candling devices to identify (distinguish between) changes in light sufficient for detection purposes, decreases significantly as the number of sheets of paper (documents) to be candled increases. More specifically, and referring now to FIG. 1 of the drawings, the curve A shows that the developed signal will tend to degrade to an extent which makes it virtually impossible to effectively detect changes in light when more than three sheets of paper are involved. This has been found to present a significant limitation to the candling of envelopes in a mail extraction procedure.
This is further complicated by irregularities resulting from differences in ambient lighting, as well as differences in the characteristics of the envelopes which are being processed (e.g., differences in construction, color, paper density and/or thickness). Such irregularities can not only further limit the ability of the system to distinguish between, or even detect a relatively large number of documents contained within an envelope, but can also limit the ability of the mail extraction device to handle different types of envelopes in a single (unified) mail extraction procedure. This can at times compromise the overall effectiveness of the mail extraction device, in some cases requiring an additional, presorting operation.
It therefore remained desirable to improve the candling techniques used in connection with a mail extraction device to facilitate the extraction process, by overcoming the above-described limitations.